The present disclosure relates to methods for reproducing content data, and specifically to a technique to reproduce encrypted content data.
In recent years, with growing need for copyright protection of content data such as video image data, content data provided with key and right information has been broadcast and distributed in terrestrial digital broadcasting, the Internet, etc. Consequently, the number of reproducing devices capable of handling content data protected by copyright has been increased, and demands for recording secure information on storage media have been increased. In a storage medium provided with a copyright protection function, mechanisms such as mutual authentication of a reproducing device and the storage medium, setting of a decryption key in an authentication area of the storage medium, and retention of right information are implemented.
In general, when content data encrypted for copyright protection is reproduced, it is often the case that decrypted plain-text content data is saved in a buffer for the purpose of, for example, smoothly performing a reproduction process. That is, in practice, the eventual security level of content data depends on products such as reproducing devices having buffers.
Conventionally, when a packet included in encrypted content data input from a network meets conditions preset in an input filter of a secure multimedia packet, a kernel level cryptographic module is invoked directly from the input filter to perform a decryption process on the encrypted content data (for example, see Japanese Unexamined Patent Publication No. 2009-194559). Then, plain-text content data generated by the decryption process is transmitted via a socket to a secure multimedia application in a user space.